This invention relates to a method and apparatus for production of a shaft having an eccentric end portion.
Such shafts are used in anti-lock braking systems, for example, although their use is obviously not limited to that particular application. The invention relates to the production of such shafts for any desired application.
Conventionally, the eccentric may be produced entirely by grinding down from the main diameter of the shaft, i.e. the shaft is mounted in an eccentric chuck, and the eccentric is ground down to its finished condition.
A much more efficient initial metal removal process is turning in a lathe. However, to polish the surface of the eccentric and to get it to the final required tolerances, a grinding operation is still required, with a fine grinding wheel.
The problem in the prior art is that to do the final grind on the eccentric, which has already been turned, the shaft has to be properly oriented in the eccentric chuck, i.e. it must be installed with the axis of the eccentric of the shaft aligned with the axis of the eccentric chuck, so that the rotation is about the axis of the eccentric of the shaft. This is obviously essential, since any wobble during grinding due to the axis of the eccentric being misaligned with the chuck axis would produce a defective part. In the prior art, the orientation has tended to be done manually, i.e. by an operating manually aligning the shaft in the chuck. This obviously leads to high labor costs and low production rates, and also to relatively high error rates since accurate manual placement is inevitably somewhat inconsistent.
There is thus a need for a means of automatically orienting the shaft properly in the eccentric chuck.